The bit-rates authorised by the digital subscriber line noted as DSL, enable high bit-rate services to be implemented. Good quality video services can thus reach the subscriber. DSL can distribute the video broadcast service, known as broadcast mode. DSL can also, owing to the possibility of using a return channel from the subscriber to the content broadcaster, allow interactive services to be set up. Video-on-demand services, noted as VoD, are thus offered to the subscriber. This involves providing a panel of videos that the subscriber can download from a content server and view on demand. Depending on the services proposed, the subscriber can view the video as is it being downloaded, in streaming mode. In this case, the video is viewed once and is not stored in the memory. According to another type of service, the subscriber can download and store the video in memory to view it subsequently one or more times, or keep it. Generally, an acknowledgement by the subscriber occurs both at the start to begin downloading and at the end of the download operation to validate the viewing of the video and subsequently leading to the payment of the service.
On the subscriber side, the video can be consulted on a computer screen. It can also be consulted on a television screen. This requires connecting the television set to a set-top box. Generally, the set-top box is connected to a modem that offers access to the VoD server via the Internet network. The set-top box can be connected to the modem by means of an Ethernet cable.
When an interruption in the VoD service occurs, the server implements a recovery on error mechanism. It uses commands of the Simple Network Management Protocol type, noted as SNMP, to restart the VoD session. This mechanism is enabled during a relatively short period that can be for example a maximum of two minutes. Beyond this period the error recovery mechanism stops; the delivery of the VoD has failed, the invoicing will be cancelled.
During the error recovery mechanism, the set-top box can switch to a back-up mode, for example by providing an access only to the reception of broadcasted video. When it receives an SNMP command from the server to recover the VoD service, it switches to VoD mode. If the VoD service is unavailable, it switches back to back-up mode. This start up operation can often lead to oscillations of the system between the broadcast video reception mode and the VoD mode.
To prevent such oscillation, one method consists of ignoring the SNMP commands. But the STB then remains in back-up mode, and cannot return to VoD mode.